Commonly assigned U.S. Pat. No. 5,422,183 describes proppants in which a microparticulate reinforcing agent is provided in the boundary region between inner and outer resin coatings. This is done by adding the reinforcing agent after the inner resin coating is applied but before it is cured, whereby the reinforcing agent becomes dispersed on and in the uncured inner resin coating. The inner resin coating is then cured, followed by addition of the outer resin coating which is also cured. The reinforcing agent enhances bonding of the inner and outer resin coatings to one another and, in addition, increases the overall strength and durability of the product proppant obtained.
In accordance with this invention, a microparticulate reinforcing agent is provided in a water-soluble external coating on a particulate proppant substrate. As a result, not only is the overall strength and durability of the inventive proppant increased, but in addition the permeability of a proppant pack formed from the inventive proppant is also enhanced. In the same way, other techniques for using a particulate material to improve the operation and/or productivity of a well in a subterranean formation can also be enhanced by this invention.
Accordingly, this invention provides a new particulate material for improving the operation and/or productivity of a well in a subterranean formation, the new particulate material comprising a subterranean particle substrate, a water-soluble external coating on the subterranean particle substrate and a microparticulate reinforcing agent at least partially embedded in the water-soluble external coating in a manner such that the microparticulate reinforcing agent is substantially released from the subterranean particle substrate when the water-soluble coating dissolves or degrades.
In addition, this invention also provides a new method for enhancing the operation and/or productivity of a well in a subterranean formation comprising introducing this new particulate material into one or more of this subterranean formation, the wellbore in this formation or the well in this formation.